http://www.james.rtsq.qc.ca/Virtgram/articlesth.htm (c) Virtual ESL Grammar

http://www.james.rtsq.qc.ca/Virtgram/aanthe.htm (c) Virtual ESL Grammar / gap-fill exercise

http://www.edufind.com/english/grammar/Determiners2a.cfm The definite article (c) Online English Grammar / Anthony Hughes

http://www.edufind.com/english/grammar/Determiners4.cfm Exceptions to using the definite article (c) Online English Grammar / Anthony Hughes

http://www.edufind.com/english/grammar/Determiners3.cfm The indefinite article (c) Online English Grammar / Anthony Hughes

http://www.aitech.ac.jp/~iteslj/quizzes/9801/cg-a_an.htm (c) Carlos Gontow / Self-Study Quizzes for ESL Students

http://www.aitech.ac.jp/~iteslj/quizzes/mc001-ck.html (c) Charles Kelly / Self-Study Quizzes for ESL Students

http://www.aitech.ac.jp/~iteslj/quizzes/js/ck/ch3-a_an_nothing.html (c) Charles Kelly / Interactive JavaScript Quizzes for ESL Students

http://www.aitech.ac.jp/~iteslj/quizzes/mc008-ld.html (c) Larry Davies / Self-Study Quizzes for ESL Students

http://www.aitech.ac.jp/~iteslj/quizzes/fb-lb-aanon.html (c) Laetitia Bradley / Self-Study Quizzes for ESL Students

http://www.aitech.ac.jp/~iteslj/quizzes/9901/cw-articles.html (c) Colleen Weldele /  Self-Study Quizzes for ESL Students

http://www.smic.be/smic5022/ (c) English Exercises Online

http://www.smic.be/smic5022/Articles2.htm (c) English Exercises Online

http://www.better-english.com/grammar/the.htm (c) better-English.com

http://www.better-english.com/grammar/the2.htm (c) better-English.com

http://www.better-english.com/grammar/the3.htm (c) better-English.com

http://www.collegeem.qc.ca/cemdept/anglais/brkfastp.htm choose a, an or some(c) ESL Blue(s)

http://www.smccd.net/accounts/sevas/esl/gramcheck/#articles (c) Grammar Check / College of San Mateo - Language Arts Division- ESL Program - English 880WW - Julie Sevastopoulos / several excellent exercises